Draw the planter's outline on the ground where you want to place it. Use chalk to draw distinct lines showing where the planter should be.
Create a trench along the chalk drawing with a small shovel. The trench should be as wide as a brick and deep enough to hold the brick with one-third of the brick above the ground. For a 3-inch-tall brick, dig a 2-inch-tall trench.
Prepare mortar according to the directions on the package. Spread it on the bottom of the trench with a trowel.
Press the bricks into the mortar, leaving a 1/2 inch gap between each brick. Continue until the trench is covered with bricks.
Fill the gap between the bricks with mortar, smoothing and wiping away mortar that gets onto the faces of the bricks. Spread a 1-inch layer of mortar on top of the first row of bricks. Immediately press more bricks on top of the mortar. Leave gaps between the bricks, as you did on the lower row, and fill them with mortar as well.
Continue to build up the walls of the planter until it's close to the desired height.
Spread mortar on the top row of bricks and place decorative brick toppers into the mortar. Let the mortar set for at least 24 hours before filling it with soil.